JP2010229431A - Ion-permeable diaphragm and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ion permeable diaphragm having a low electric resistance and capable of improving the separation performance of a gas (hydrogen, oxygen or the like) produced on the other side of the diaphragm, to be used in alkaline water electrolytic device, and to provide a production method of the ion permeable diaphragm. <P>SOLUTION: The ion permeable diaphragm 1 used for alkaline water electrolysis includes a membrane material 1A containing a calcium phosphate compound (fluoroapatite, hydroxyapatite or the like) or calcium fluoride as a hydrophilic inorganic material, wherein the average particle diameter of the hydrophilic inorganic material is not more than 0.7 μm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an ion permeable diaphragm for use in an alkaline water electrolysis apparatus, and more particularly to an ion permeable diaphragm for use in an alkaline water electrolysis apparatus having a structure in which an ion permeable diaphragm is sandwiched between electrodes and a method for manufacturing the same. About.

  Reflecting the recent energy situation, hydrogen is attracting attention from various fields as a new energy source to replace oil. Examples of such industrial production methods of hydrogen include coke and petroleum gasification methods, water electrolysis methods, and the like.

  The former method has a problem that the operation is complicated and a very large-scale facility is required, so that the initial cost is considerably increased.

  On the other hand, the latter method uses readily available water as a raw material, and a plurality of electrode pairs are provided in an electrolytic cell, and an alkaline electrolyte such as KOH is circulated between these electrodes and ion permeation is performed. The membrane is divided by a permeable membrane to generate hydrogen on the cathode side and oxygen on the anode side of the ion permeable membrane, but there is an ion permeable membrane and an electrolyte solution between the electrodes. Therefore, there are problems that electric resistance is large and electrolysis efficiency is poor. However, since this water electrolysis method can generate hydrogen even in a relatively small facility and is practical, improvement in electrolysis efficiency is desired.

By the way, the following performance is required for a diaphragm used in an electrochemical electrolytic cell represented by such an alkaline water electrolysis apparatus.
(1) Pass only ions through the membrane and do not allow gas to pass or diffuse (2) Be physically and chemically durable in the electrolyte (3) Low electrical resistance

  As a diaphragm for electrolysis having such performance, asbestos cloth is widely used practically. However, despite the fact that the electrolyte solution sometimes exceeds 100 ° C, asbestos cloth cannot be used due to corrosion at temperatures of 100 ° C or higher, and in recent years there have been many reports of health damage caused by asbestos. There is a big problem with its use.

  Therefore, while satisfying the above performances (1) and (2), and (3) a polymer porous membrane, an ion exchange membrane, or a metal oxide membrane such as NiO as an ion permeable membrane having a lower electrical resistance. (See Patent Document 1) and ion-permeable diaphragms (see Patent Document 2) using a composite material of an inorganic substance and an organic polymer as a diaphragm material have been proposed.

Japanese Examined Patent Publication No. 62-50557 Japanese Patent No. 2607734

  However, among the ion permeable membranes made of each of the above membrane materials, the polymer porous membrane has the advantage that it is flexible and highly resistant to mechanical damage, but the polymer material used here is Since it is hydrophobic, there is a problem that even if it is porous, movement of ions solvated in the electrolyte is not easy, electric resistance increases, and the performance of the electrolytic cell is severely degraded. In addition, in a polymer porous membrane or an ion exchange membrane, in an alkaline water electrolysis device that generates gas, there is a problem that gas bubbles adhere to the surface of the membrane and electrical resistance increases, and in particular, bubbles are concentrated. In particular, when the electrical resistance greatly increases, there is a problem that a high temperature portion called a so-called hot spot is generated and the diaphragm is deteriorated.

  Further, a metal oxide film such as NiO described in Patent Document 1 is manufactured by sintering, but a dense sintered diaphragm without gas diffusion or permeation has a limit in size. Therefore, there is a problem that it is not suitable for application to a large electrolytic cell.

  And the ion-permeable membrane which used the composite material of the inorganic substance and organic polymer described in patent document 2 as a membrane uses zirconium oxide, polyantimonic acid as an inorganic wettable material, fluorocarbon polymer, polysulfone, etc. Are formed as a binder to form fine pores. An ion-permeable diaphragm using this composite material exhibits excellent smoothness and very good ion conductivity, and is suitable as a diaphragm for an alkaline water electrolysis apparatus.

  However, although the inorganic wettable material used for the ion permeable diaphragm described in Patent Document 2 has wettability, the gas is separated when the differential pressure increases across the ion permeable diaphragm. There is a problem that it becomes difficult.

  The present invention solves the above-described conventional problems, and is used in an alkaline water electrolysis apparatus that has low electrical resistance and can improve the separation performance of gas (hydrogen, oxygen, etc.) generated across a diaphragm. It is an object of the present invention to provide an ion-permeable diaphragm and a method for producing the ion-permeable diaphragm.

  In order to solve the above-mentioned problems, the present invention is an ion-permeable diaphragm used for alkaline water electrolysis, comprising a membrane material containing a calcium phosphate compound or calcium fluoride as a hydrophilic inorganic material, and the hydrophilic inorganic Provided is an ion-permeable diaphragm characterized in that the average particle size of the material is 0.7 μm or less.

  According to the above invention (Invention 1), the average particle size of the hydrophilic inorganic material is 0.7 μm or less, so that a dense pore structure is formed, so that the gas separation performance can be improved. As a result, oxygen generated on the anode side is not mixed with hydrogen generated on the cathode side of the ion-permeable diaphragm, and the purity of hydrogen can be maintained high. In addition, since ions in alkaline water electrolysis can quickly pass through ion-permeable membranes with increased hydrophilicity, the electrical resistance of the membrane itself can be reduced, thereby consuming when used in alkaline water electrolysis devices. Electric power can be reduced and electric field efficiency can be improved.

  In the said invention (invention 1), it is preferable that the calcium phosphate compound as the hydrophilic inorganic material is fluoroapatite (FAP) or hydroxyapatite (HAP) (invention 2). Moreover, in the said invention (invention 1-2), the said membrane material is the said hydrophilic inorganic material, and at least 1 sort (s) of organic binding material selected from the group which consists of a polysulfone, a polypropylene, and polyvinylidene fluoride. It is preferable that an organic fiber cloth is contained in the mixture (claim 3). Furthermore, in the said invention (invention 3), it is preferable that the said organic fiber cloth is a mesh of polypropylene (invention 4).

  According to the above inventions (Inventions 2 to 4), the membrane material itself has very good hydrophilicity and excellent ionic conductivity, so that it is suitable as a diaphragm for an alkaline water electrolysis apparatus. be able to.

  In the said invention (invention 1-4), it is preferable that the thickness of the said film | membrane material is 100 micrometers or more (invention 5). By increasing the thickness of the film material, the desired film strength can be secured, while the electric resistance of the film may increase. According to this invention (claim 5), Since it has good hydrophilicity and excellent ionic conductivity, the electrical resistance of the film does not increase even if the thickness of the film material is increased to a certain level, and the desired film strength can be secured. it can.

  Further, the present invention is a method for producing an ion permeable membrane according to the above inventions (Inventions 1 to 5), wherein the hydrophilic inorganic material and the organic binding material having an average particle size adjusted to 0.7 μm or less, A method for producing an ion permeable membrane is provided, wherein an organic fiber cloth is soaked in a wet sheet produced from a suspension containing a liquid crystal (claim 6).

  According to the above invention (invention 6), by using a hydrophilic inorganic material having an average particle diameter adjusted to 0.7 μm or less, a dense pore structure is formed, so that gas separation performance is improved. It is possible to produce an ion permeable diaphragm that can maintain high purity of hydrogen without mixing oxygen generated on the anode side with hydrogen generated on the cathode side of the ion permeable diaphragm. .

  In the above invention (invention 6), an average particle size of 0.7 μm or less is obtained by introducing an organic binder solution obtained by dissolving the organic binder in an organic solvent and a hydrophilic inorganic material into a bead mill. It is preferable to prepare a suspension containing the adjusted hydrophilic inorganic material and the organic binder (claim 7).

  When the hydrophilic inorganic material is pulverized by, for example, a ball mill, the pulverization takes a period of one week or more, and the average particle size of the hydrophilic inorganic material after pulverization is about 4 μm, so that the gas separation performance is insufficient. The hydrogen generated on the cathode side of the ion-permeable membrane may be mixed with oxygen generated on the anode side. According to the invention (invention 8), the organic binder solution and the hydrophilicity are contained in the bead mill. By introducing and mixing with an inorganic material, an ion-permeable membrane including a hydrophilic inorganic material with an average particle size adjusted to 0.7 μm or less and improved gas separation performance can be easily and quickly. Can be manufactured.

  According to the present invention, an ion-permeable diaphragm for use in an alkaline water electrolysis apparatus having low electrical resistance and improved separation performance of gas (hydrogen, oxygen, etc.) generated across the diaphragm, and the ion permeation A method for producing a sex diaphragm can be provided.

It is an expanded sectional view showing one unit of an electrolysis unit of an alkaline water electrolysis device using an ion permeable diaphragm concerning one embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is an enlarged cross-sectional view showing one unit of an electrolysis unit of an alkaline water electrolysis apparatus using an ion permeable diaphragm according to an embodiment of the present invention.

  In FIG. 1, the ion-permeable diaphragm 1 is held in a form sandwiched between mesh-like electrodes 2 and 3, and these mesh-like electrodes 2 and 3 are connected via conductive members 2A and 3A. The bipolar electrodes 4 and 5 are connected to the anode side 4A and the cathode side 5A, respectively. Thereby, a voltage is applied between the ion permeable diaphragms 1. In this embodiment, as shown in FIG. 1, the ion permeable diaphragm 1 has an electrolytic cell 6 in the electrolytic cell 6 in which the potassium hydroxide (KOH) solution as the alkaline solution W is accommodated. It is arranged so as to be divided into a side and a cathode side.

  As the membrane material 1A for forming the ion permeable diaphragm 1, only ions are allowed to pass through the membrane, there is no gas passage or diffusion, and the material is physically and chemically durable in the alkaline solution W. If there is, there is no particular limitation.

  For example, the membrane material 1A was stretched into a film-forming mixture containing a hydrophilic inorganic material and at least one organic binder selected from the group consisting of polysulfone, polypropylene, polyvinylidene fluoride, and the like. It is preferable to use an organic fiber cloth.

  As the hydrophilic inorganic material, a calcium phosphate compound such as fluoroapatite (FAP) or hydroxyapatite (HAP) is preferably used, and these hydrophilic inorganic materials are preferably used in the form of granules. The average particle size of the particles of the hydrophilic inorganic material is 0.7 μm or less, and particularly preferably 0.5 μm or less.

As the hydrophilic inorganic material other than the calcium phosphate compound, it can be preferably used calcium fluoride (CaF _2). This calcium fluoride also has an average particle size of 0.7 μm or less, particularly 0.5 μm or less, like the above-mentioned calcium phosphate compound. Moreover, this calcium fluoride can utilize what is marketed as an industrial chemical, and can utilize what is collect | recovered industrially. For example, in the treatment process of fluorine-containing wastewater, fluorine is removed after being fixed as CaF _{2 and} can be reused.

Further, as the organic fiber cloth, a mesh made of polypropylene, a mesh made of a pre-halogenated ethylene copolymer such as ethylene and monochlorotrifluoroethylene, or the like can be used. As this organic fiber cloth, a woven fabric or a non-woven fabric can be used. The fiber diameter is preferably 1 mm or less, and particularly preferably the fiber diameter is 0.5 mm or less. No particular limitation is imposed dimensions of weave of the organic fiber fabric, it is preferred preferably at 4 mm ² or less, in particular 1 mm ² or less.

The film material 1A composed of the hydrophilic inorganic material, the organic binding material, and the organic fiber cloth as described above can be manufactured as follows, for example.
First, an organic binder solution obtained by dissolving an organic binder in an organic solvent, a hydrophilic inorganic material, and a medium medium (beads) are put into a bead mill and stirred. Thereby, while being able to adjust the average particle diameter of a hydrophilic inorganic material to 0.7 micrometer or less, the suspension liquid (slurry) containing the said hydrophilic inorganic material and an organic binding material can be prepared.

  As the organic solvent, for example, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, mono- and diethers of ethylene glycol, or ketones such as methyl ethyl ketone can be used.

The blending ratio of the hydrophilic inorganic material (FAP, HAP, CaF ₂ ) and the organic binding material is preferably 10 to 95% by mass, more preferably 40 to 90% by mass of the hydrophilic inorganic material. More preferred is 75 to 85% by mass. When the blending ratio of the hydrophilic inorganic material is less than 10% by mass, the electric resistance of the obtained membrane material 1A itself is increased, which is not preferable from the viewpoint of the electric resistance of the ion-permeable diaphragm 1 using the same. On the other hand, if the blending ratio of the hydrophilic inorganic material exceeds 95% by mass, the mechanical strength of the film material 1A, particularly the brittleness, becomes too low, and it may be difficult to maintain the form as a film.

  In addition, there exists a tendency for the wettability (hydrophilicity) of a film | membrane material to become high and the electrical resistance of a film | membrane to become low, so that there are many compounding ratios of a hydrophilic inorganic material with respect to an organic binding material. In particular, hydroxyapatite (HAP) as a hydrophilic inorganic material has a lower electrical resistance as the blending ratio is higher, but is poorly mixed with an organic binder and an organic solvent, and compared with fluoroapatite (FAP). In the same mass%, the slurry has a high viscosity and is easily separated. For this reason, when using a hydroxyapatite (HAP) as a hydrophilic inorganic material, it is preferable to prepare a slurry with a blending ratio of hydroxyapatite (HAP) of at most about 60 to 70% by mass.

  In addition, fluoroapatite (FAP) as a hydrophilic inorganic material has a good mixing property with an organic binder and an organic solvent, and a slurry can be prepared at a blending ratio of 10 to 95% by mass as described above. It is preferable to prepare the slurry at an optimum blending ratio of 75 to 85% by mass.

  Therefore, it is preferable to use fluoroapatite (FAP) from the viewpoint of handling as the hydrophilic inorganic material used for the membrane material.

  In addition, the compounding ratio of the organic solvent should just be 40 mass% or more in a total of 100 mass% with the organic binder which is a film formation substance. In addition, the thickness of the wet sheet to be manufactured is preferably 2 mm or less, and particularly preferably 1.5 mm or less.

  As the medium medium (beads) put into the bead mill, for example, zirconia beads, alumina beads, glass beads and the like can be used. What is necessary is just 5 mm or less. If the particle size of the beads exceeds φ1 mm, it may be difficult to adjust the average particle size of the hydrophilic inorganic material to 0.7 μm or less.

  Further, the mixing ratio of the medium media (beads) is not particularly limited, but may be about 2 to 4 times (mass basis) with respect to the hydrophilic inorganic material. If the blending ratio of the beads is within the above range, the average particle diameter of the hydrophilic inorganic material can be efficiently adjusted to 0.7 μm or less.

  When mixing a hydrophilic inorganic material and an organic binder solution in a bead mill, the stirring speed of the mill is a suspension (slurry) containing a hydrophilic inorganic material having an average particle size of 0.7 μm or less and an organic binder. It is not particularly limited as long as it can be prepared. For example, it may be set to about 1000 to 5000 rpm, and the processing time may be about 0.5 to 3 hours.

  The suspension (slurry) thus obtained is uniformly applied to a predetermined thickness on a smooth surface made of an inert material such as a glass plate to produce a wet sheet. Then, the organic fiber cloth is immersed in this wet sheet in a stretched state, and the organic solvent is removed by evaporation or leaching in a water bath while maintaining the stretch of the organic fiber cloth. 1A is peeled off.

  The thickness (t) of the film material 1A produced in this way is preferably 100 μm or more, particularly 300 to 600 μm. If the thickness of the membrane material 1A is less than 100 μm, the membrane strength as the membrane material 1A for alkaline water electrolysis may not be sufficient. Even if the thickness of the film material 1A is 100 μm or more, the electrical resistance of the film material 1A does not increase, and excellent ion conductivity can be achieved.

Ion-permeable membrane 1 as described above, KOH solution of 1 mol / L, under the conditions of 25 ℃, 0.20Ωcm ² below, in particular a 0.15Omucm ² below the membrane resistance (electrical resistance).

In the electrolysis unit shown in FIG. 1 using such an ion-permeable diaphragm 1, when a current is passed through the bipolar electrodes 4 and 5, a voltage is generated between the conductive members 2A and 3A and the mesh-like electrodes 2 and 3, Electrolysis of the potassium hydroxide solution W generates oxygen (O ₂ ) at the interface between the ion permeable diaphragm 1 and the mesh electrode 2 (anode).

Then, twice the amount of hydrogen (H ₂ ) is generated at the interface between the ion permeable diaphragm 1 and the mesh electrode 3 (cathode). Since the electrolytic cell 6 in this electrolysis unit is partitioned into the cathode side and the anode side by the ion permeable diaphragm 1, high-purity hydrogen gas is efficiently produced by recovering only hydrogen generated on the cathode side. can do.

  At this time, the ion permeable diaphragm 1 contains an inorganic material (inorganic wettable substance) excellent in hydrophilicity, and the membrane material 1A has a porous structure, so that a potassium hydroxide solution is obtained. Since ions therein move quickly, the electrical resistance of the ion-permeable diaphragm 1 is reduced, and alkaline water electrolysis can be performed efficiently.

  In addition, the average particle size of the hydrophilic inorganic material in the membrane material 1A is adjusted to 0.7 μm or less, and the ion-permeable diaphragm 1 has a dense pore structure, so that the solution is free from the ion-permeable membrane 1. Although it can pass through, the bubbles of oxygen gas generated on the anode side and the bubbles of hydrogen gas generated on the cathode side cannot pass through, so there is no possibility that these gases are mixed with each other. Therefore, the purity of the hydrogen gas obtained from the cathode side can be kept extremely high.

  The embodiment described above is described for facilitating understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example and a comparative example, this invention is not limited to the following Example at all.

[Example 1] Production of atomized CaF ₂ -containing membrane material 54 g of polysulfone (manufactured by Solvay Advanced Polymers, P-3500) was added to 546 g of N-methyl-2-pyrrolidone (manufactured by Kishida Chemical, special grade, NMP) in vacuum. (−0.1 MPa) was completely dissolved.

The obtained solution was transferred to a vessel of a bead mill (manufactured by Ashizawa Finetech Co., Ltd., Minizea), and 485 g of zirconia beads (particle size: 0.5 mm) were added, and 192 g of CaF ₂ was added as a hydrophilizing material. Then, the mill was stirred at 3900 rpm for 1 hour. The power of the mill at this time was 1.12 kWh. Moreover, the average particle diameter of the obtained CaF ₂ was 0.7 μm.

The suspension thus obtained was placed in a stretched state with a 200 mesh polypropylene fiber cloth (fiber diameter: 87 μm, manufactured by NBC, trade name: nip (polypropylene) strong net) at a position of 400 μm from the bottom. 10 mL was poured on a 10 cm × 10 cm glass frame to prepare a wet sheet having a surface area of 100 cm ² and a thickness of about 500 μm.

  Immediately after pouring the suspension, the frame was transferred into an IPA bath and allowed to stand overnight at room temperature, and N-methyl-2-pyrrolidone (NMP) as a solvent was leached from the wet sheet. Thereafter, the sheet remaining on the frame was peeled off and held for 5 minutes in water to obtain a sheet-like film material. The obtained sheet-like membrane material had a thickness of about 400 μm.

Comparative Example 1 was repeated except for pulverizing the CaF ₂ as a hydrophilic material using a ball mill instead of manufacturing a bead mill of CaF ₂ containing film material, to produce a sheet-like film material in the same manner as in Example 1. The average particle diameter of the obtained CaF ₂ was 1.0 μm.

[Electrical resistance measurement test]
The ion permeable membranes of Example 1 and Comparative Example 1 obtained as described above were immersed in a 1 mol / L KOH solution, and a resistance measuring instrument was used for these ion permeable membranes at 25 ° C. and 1000 Hz alternating current. Membrane resistance was measured using (Hioki Electric Co., Ltd., LCR HiTester 5030).
The results are shown in Table 1.

[Gas permeability test]
The ion permeable diaphragm 5 of Example 1 and Comparative Example 1 was installed in the electrolytic unit shown in FIG. 1, N ₂ gas was introduced from the H ₂ side, and the pressure at which leakage started on the O ₂ side was measured.
The results are shown in Table 1.

As shown in Table 1, the electrolysis unit using the ion permeable membrane of Example 1 has a very low membrane resistance of 0.2 Ω · cm ² or less, and also has a very high leak pressure from the H ₂ side. It was high and it was confirmed that the gas permeation characteristics were also excellent.

DESCRIPTION OF SYMBOLS 1 ... Ion-permeable diaphragm 1A ... Membrane material 2 ... Electrode (anode)
2A ... conductive member 3 ... electrode (cathode)
3A ... conductive members 4, 5 ... bipolar electrode 6 ... electrolytic cell W ... potassium hydroxide (KOH) solution (alkali solution)
t: thickness of membrane material

Claims (7)

An ion permeable membrane used for alkaline water electrolysis,
A membrane material containing a calcium phosphate compound or calcium fluoride as a hydrophilic inorganic material,
An ion-permeable diaphragm, wherein the hydrophilic inorganic material has an average particle size of 0.7 μm or less.   The ion-permeable diaphragm according to claim 1, wherein the calcium phosphate compound as the hydrophilic inorganic material is fluoroapatite or hydroxyapatite.   The membrane material is a mixture of the hydrophilic inorganic material and at least one organic binding material selected from the group consisting of polysulfone, polypropylene, and polyvinylidene fluoride, with an organic fiber cloth incorporated therein. The ion permeable membrane according to claim 1 or 2, characterized by the above.   The ion permeable membrane according to claim 3, wherein the organic fiber cloth is a polypropylene mesh.   The ion permeable membrane according to any one of claims 1 to 4, wherein the membrane material has a thickness of 100 µm or more. A method for producing the ion-permeable membrane according to any one of claims 1 to 5,
Manufacture of an ion permeable membrane characterized by immersing an organic fiber cloth in a wet sheet manufactured from a suspension containing a hydrophilic inorganic material and an organic binder having an average particle size adjusted to 0.7 μm or less Method.   An organic binding material solution obtained by dissolving the organic binding material in an organic solvent and a hydrophilic inorganic material are introduced into a bead mill, and the organic inorganic bond and the hydrophilic inorganic material whose average particle size is adjusted to 0.7 μm or less A method for producing an ion-permeable diaphragm according to claim 6, wherein a suspension containing the material is prepared.

Images